Online Papers - Brian Weatherson

Scepticism, Rationalism and Externalism 203
been a proposition about the present that we cannot directly perceive, such as that
it is not snowing in Sydney right now, the rest of the argument would have been
unaffected. The summary here is that if one is suitably externalist about perception,
so one thinks the existence of perceptual states entail the existence of the things being
perceived, one can accept this argument, accept internalism, accept empiricism, and
not be an external world sceptic. For it is consistent with such a position that one
know the existence of the things one perceives. But on this picture one can know
very little beyond that, so for most practical purposes, the position is still a sceptical
one.
The externalist response is more interesting. Or, to be more precise, the externalist
reponses are more interesting. Although I have appealed to internalism a couple of
times in the above argument, it might not be so clear how the externalist can respond.
Indeed, it may be worried that by exercising a little more care in various places I could
have shown that everyone must accept either rationalism or scepticism. That is the
conclusion Hawthorne derives in his paper on deeply contingent a priori knowledge,
though as noted above he uses somewhat more contentious reasoning than I do
in order to get there. To conclude, I will argue that the internalism is crucial to the
argument I have presented, and I will spell out how the externalist can get out of the
trap I’ve set above.
One easy move that’s available to an externalist is to deny that any facts about
justification are a priori. That blocks the move that says we can find a G such that
it’s a priori that anyone whose evidence is G can know that it will snow in Ithaca
next year. This is not an essential feature of externalism. One can be an externalist
about justification and still think it is a priori that if one’s evidence has the property is
reliably correlated with snow in the near future then it justifies belief that it will shortly
snow. But the position that all facts about justification are a posteriori fits well with
a certain kind of naturalist attitude, and people with that attitude will find it easy to
block the sceptical argument I’ve presented.
Can, however, we use an argument like mine to argue against an anti-sceptic empiricist
externalist who thinks some of the facts about justification can be discovered
a priori? The strategy I’ve used to build the argument is fairly transparent: find a disjunctive
a priori knowable proposition by partitioning the possible evidence states
into a small class, and adding a disjunct for every cell of the partition. In every case,
the disjunct that is added is one that is known to be known given that evidence. If
one of the items of knowledge is ampliative, if it goes beyond the evidence, then it is
possible the disjunction will be deeply contingent. But the disjunction is known no
matter what.
If internalism is true, then the partition can divide up evidential states according
to the introspective properties of the subject. If externalism is true, then such a partition
may not be that useful, because we cannot infer much about what the subject
is justified in believing from the introspective properties she instantiates. Consider,
for example, the above partition of subjects into the G and the not-G, where G is
some introspective property, intuitively one somewhat connected with it snowing in
Ithaca next year. The subjects that are not-G know that they don’t know they know